It is November, and most ballerinas are getting ready for the seasonal round of Nutcrackers. Tamara Rojo, however, won't be among them. She grins with delicate malice. "The Sugar Plum Fairy isn't my favourite role. She's so vacuous, a character with no past and no future."

But the main reason for Rojo's absence from the stage this Christmas is the fact that she's spending most of December in Canada, on a work placement with the country's National Ballet, shadowing its director Karen Kain; she is learning how to become an artistic director. Still in her mid-30s, and still one of the Royal Ballet's star principals, Rojo is nonetheless planning her second career.

Traditionally, when ballerinas retired, they married, or started up dance schools. Today, the choices are wider. Darcey Bussell (40) is alternating motherhood with guest appearances on Strictly Come Dancing, as well as designing children's dancewear; Sylvie Guillem (44) has opted for a late flowering as a modern dancer, working on experimental projects with Akram Khan, Russell Maliphant and Robert Lepage.

Still, few ballerinas dream of a life of meetings and boardrooms. And when I meet Rojo, it's hard to see her as anything other than a working dancer. Her skin has that translucent, exhausted pallor that comes from spending hours inside a rehearsal studio; the black practice tutu she dumps on the sofa looks more natural to her than a briefcase. She readily admits that the idea of becoming an artistic director was not her own. "It was forced on me, really – when people started using my name in discussions about forming a new company in Spain."

Spain is exceptional among developed countries in having no national ballet; most of its state funding has been channelled into flamenco and modern dance. The majority of its classical dancers have to travel abroad to work, something that Rojo, who came to Britain when she was 22, regards as a scandal. "Ballet dancers in my country have been condemned to emigrate, year after year, decade after decade."

It came as a shock to her when, three and a half years ago, the Spanish government suggested it would fund a new ballet company if Rojo came home to run it. "I thought maybe this was my responsibility. Maybe the fact that I have become Spain's most famous ballerina means I have to give something back." She was asked to submit a proposal for a national company, which she sees as following the Royal Ballet model, building up a repertory of new and classic works.

Talks with the government are still under way, but a couple of years ago Rojo began to study for such a move, enrolling for a part-time performing arts degree at Madrid University. She continued to dance a full schedule with the Royal Ballet, but flew to Madrid once a month to meet with her tutors. She also started to ask questions about how the Royal is run, surprising board members with requests to attend meetings.

Rojo has attached one absolute condition to her acceptance of the government's offer: Spain must change its system of arts funding. "It's completely totalitarian," she says, with contempt. "There is no arts council, there are no company boards, which means companies are always being manipulated by politicians. I've said the only way I would direct a company in Spain is if they set up an arts council. The government have to reassure me that this is a long-term project. If I'm going to sacrifice my dancing career, I have to know that in three years' time some politician won't come along and put his cousin in my place."

Rojo is pessimistic about the chances of Spain changing its arts funding just for her; if not, she hopes some other company will eventually employ her. "Directing jobs are very few," she admits. "It's a very unsafe career decision. But it has become my passion."

If she does move to Spain and stop dancing, it will be quite a sacrifice. On stage, Rojo's technical rigour is a constant pleasure. She is not a flashy dancer; her radiance has a pearly quality rather than a diamante dazzle. Yet however soft she may appear, she can be relied on to pull off a perfect quadruple pirouette or a rock-solid balance. Her control can be almost eerie. "Sometimes it's like I'm outside myself," she says, "watching the movement come out of my body. There are no nerves. It feels like an amazing freedom."

She swears that such moments are the result of pure hard work (she likes the theory that it takes 10,000 hours of work to produce a genius, laughing that she has probably put in 50,000). But Rojo's other exceptional quality is her vivid, imaginative investment in each role. She will research every detail of an interpretation, drawing on theatre, film, and on curator friends such as Jay Jopling and Norman Rosenthal. "I need to create pictures, smells and sounds for my characters. I need to know what Mary Vetsera would hear [in Mayerling] when she arrives in the carriage to face Rudolf."

Issuing an ultimatum to the Spanish government may sound like an unusually robust act for a ballerina, but Rojo does have politics in her blood. Her father, an industrial engineer, and her mother, a finance director, were both passionately engaged with the resurgence of Spain's political left after the death of Franco, and took their only daughter everywhere with them. "Some of the earliest photos of me are taken on a march, sitting on my dad's shoulders, waving a flag," Rojo says proudly. She was taken to party meetings, absorbing the rhetoric of political speeches at an age when most children are listening to fairytales. Unsurprisingly, her parents "weren't too excited" when, at the age of five, she announced she wanted to be a ballerina. The epiphany came when she was waiting for her mother to pick her up from school. "It was raining and cold so my teacher told me to come into the gym. There was a ballet class going on and that was it. I knew." Back then, she thought being a ballerina just meant "going to ballet class for the rest of your life. It was the intimacy of class I loved – just you, your body and the piano music. When my mum took me to see my first ballet, Swan Lake, I was so disappointed. It seemed rather vulgar."

The hothoused nine-year-old

She was, she says, a dreamy, solitary child: "I had a world inside my head where everything was quiet." At the age of nine, she was enrolled at the private Victor Ullate ballet school in Madrid, one of Spain's best, where she took an exhausting six hours of ballet tuition every day, on top of normal school. "There were no health and safety regulations," she recalls. "No one suggested it was too much for a child, but it gave me stamina and resilience. Ballet is very logical: the more you do, the more your body works it out."

By the time Rojo was 16, she had a technical assurance far beyond her years. She took lead roles in Ullate's small company and won a major competition in Paris. Even when her career took off, she continued to take extra classes in her spare time. "I wanted to go on stage and know that I wouldn't have to worry about holding an arabesque. It's the same as being a good artisan. When a glassmaker puts his glass in the oven, he has to know it won't come out cracked."

It troubles her that the Royal, like all big companies, has become so time-pressured. This year she gave up her summer holidays to work with choreographer Kim Brandstrup, on a project that allowed her to get creatively involved in characterisation and choreography from the start. The work, Goldberg Variations, drew on the dynamics of the rehearsal studio, which fascinate Rojo. "The characters you see on stage have often been strongly influenced by what's happened in the studio – who's been having an affair with who, who's broken up with who." Rojo's performance showcased her ability to project thought and emotion, even when motionless on the sidelines. Creating her own role was "fantastic", Rojo says, though she admits she found parts of the process preposterously slow. "We'd spend an hour discussing one point, and I'd be thinking, 'I could have rehearsed all of Sleeping Beauty in this time.'"

Dancing, says Rojo, "gets easier as you get older – you feel freer". And she's not yet suffering either the physical depredations or the broodiness that leads other ballerinas to retire. "I'm not thinking about babies yet," she says cheerfully. "And I don't know anyone who wants to have them with me."